León Ferrari's "Branches," part of MoMA's retrospective.

At first look, artist León Ferrari’s "Letters to a General" seems like large, written text with exaggerated calligraphy. But looking closely, there are no words, just a mass of illegible scribbles.

The piece from the 89-year-old Argentine is part of the Museum of Modern Art’s "Tangled Alphabets," a dual retrospective on Ferrari and the late Swiss artist Mira Schendel, who died in Brazil in 1988 after living there for 40 years.

Ferrari, who fled Argentina’s military junta in 1976 and had a son who "disappeared," has explained "Letters" by saying, "How can you speak logically to a general?"

His work may be abstract, said the show’s curator, Luis Pérez-Oramas, but he uses the style as a tool for a concrete political message.

In the collage "Rereadings of the Bible," Jesus is shown crucified on a war plane in free fall. "Last Judgment," a reproduction of Michelangelo’s Sistine Chapel masterpiece, is covered with bird poop.

Because Ferrari’s work has been critical of the Argentine government and the Catholic Church’s complicit role during the dictatorship, it has not escaped controversy back home.

The MoMA exhibit, which includes 200 drawings, paintings and other works and is on view through June 15, is the first major U.S. show for either Ferrari or Schendel.

"[They] are among the most important artists of the 20th century anywhere in the world," said MoMA’s director, Glenn Lowry.

Language is at the center of both artists’ work, as the MoMA retrospective easily conveys.

"They worked during the same years; they thought about similar problems," said Pérez-Oramas, the first curator of Latin-American art at MoMA. "They used language as if there is no distinction between the visible and the legible."

Schendel was raised in Italy but she immigrated to Brazil, where she became a painter and a professor.

In the series "Graphic Objects," Schendel displays letters, symbols and signs on thin Japanese paper between transparent acrylic sheets that allow the work to be seen at both sides.

"Outstanding creators are rare," says the Venezuelan-born Pérez-Oramas. "This is an opportunity to meet the work of two artists that is unseen and familiar at the same time."